Barbara L. Sherriff

PRECIPITATION OF IRON MINERALS BY A NATURAL MICROBIAL CONSORTIUM

Abstract A microbial biofilm consortium enriched from Shield surface water is able to mediate geochemical cycling of iron within a biofilm. Iron can be leached from Fe(II) containing minerals such as magnetite, biotite and ilmenite to generate a colloidal Fe(III) suspension. The Fe(III) can then be reduced back to Fe(II) by iron-reducing bacteria that utilize it as an electron acceptor. On precipitation, different iron compounds are formed depending on the ratio of iron to carbon in the media and upon the local environment. Mossbauer and X-ray diffraction spectroscopy show these compounds to include ferrous hydroxide, vivianite, ferrihydrite and hematite. These minerals may then become incorporated into stratifer iron deposits such as Banded Iron Formations.

One person's food: how and why fish avoidance may affect the settlement and subsistence patterns of hunter-gatherers.

Foraging strategies of modern hunter-gatherers may not accurately model resource use of specialized big-game hunters. Historic accounts from the Northern Plains of North America indicate that utilization of spring-spawning fish when large mammals were fat-depleted was not universally beneficial. Three independent reports from Europeans and Americans show that a sudden switch from a prolonged diet of lean red meat to fish produces symptoms consistent with lipid (fat) malabsorption. It is hypothesized that plains-adapted hunter-gatherers formed their camps in grassland environments and hunted big game throughout the winter The effects of eating lean meat alone were avoided by utilizing fetal and newborn animals and through the use of stored carbohydrate-rich foods. Groups associated with wooded environments wintered along the margins of the winter grazing range. They followed a diverse strategy with opportunistic use of big game and were able to exploit spring-spawning fish. Archaeological remains from 18 sites from the plains, parkland, and forests of Western Canada were used to test these hypotheses. The faunal assemblages, tools, and identifications of lipid residues from pottery vessels were consistent with the proposed strategies.

MICROBIAL TRANSFORMATION OF MAGNETITE TO HEMATITE

Abstract A microbial consortium enriched from surface water draining the Lac du Bonnet granitic batholith in Manitoba, Canada, was able to mediate the transformation of 11 % of the Fe in a sample of magnetite into hematite within three weeks. Holes, up to 100 μm in diameter, were formed in grains of magnetite in a polished section of granite that had been exposed to a microbial biofilm in the laboratory. Bacteria were seen by scanning electron microscopy to be attached to magnetite after three days incubation in a flask, while a covering of biofilm was nearly complete after six days. Some hexagonal grains of an iron mineral were visible after incubation for eight weeks. Dissolution of the magnetite and the presence of hematite in the incubated flasks was confirmed by Mossbauer spectra and powder X-ray diffraction patterns. No hematite was found either in the original sample of magnetite or in duplicate sterile controls.

Substitutional mechanisms, compositional trends and the end-member formulae of scapolite

Compositional trends of natural samples of scapolite extend toward the ideal (anhydrous) end-members marialite (Ma) Na4Al3Si9O24Cl and meionite (Me) Ca4Al6Si6O24CO3. Intermediate members do not follow the plagioclase substitution, although Si contents closely correlate with Me% [calculated as 100{Σ(divalent cations)}/4]. The solid solution may be explained by substitutional interactions among the M, T and A sites, as constrained by net charge-balance and maximum site-occupancy requirements of the structural formula M4T12O24A. Two changes in compositional trends located at [(Na3.4Ca0.6)(Al3.6Si8.4)O24]+1 and [(Na1.4Ca2.6)(Al4.7Si7.3)O24]+1.9 divide the series into three portions. Nomenclature consistent with these divisions is marialite (Me 0–15), calcian marialite (15 < Me ≤ 50), sodian meionite (50 < Me < 65) and meionite (Me 65–100). A large number of scapolite occurrences have Si values near 7.3 apfu, corresponding to the 14/m-P42/n symmetry transition and to the stabilization of scapolite in a Cl-poor environment. Trends of Cl with Si or (Na + K) apfu indicate complex substitutional mechanisms, and should not be used to suggest that “mizzonite” or “dipyre” are end-members. Calculation of excess positive charge from measurement of M and T cations indicates that scapolite typically has the maximum content of Cl expected by charge-balance. Anion substitution is complicated by substition of H as hydroxyl or bicarbonate-bisulfate anions. The calculation CO2 = 1−ClFS may apply only to anhydrous scapolites which are rare, otherwise it over-estimates CO2 because it ignores the role of H. CO2 content calculated by charge-balance equations gives better agreement with constraints of the known substitutional mechanism. More H is present than is required by stoichiometry, and molecular H2O may be present in channels along the c-axis.

Silvialite, a new sulfate-dominant member of the scapolite group with an Al-Si composition near the 14/m-P4 2 /n phase transition

Abstract Silvialite, ideally Ca4Al6Si6O24SO4, is tetragonal, I4/m, Z = 2, with a = 12.160(3), c = 7.560(1) Å, V = 1117.9(8) Å3, c:a = 0.6217:1, ω= 1.583, Ɛ= 1.558 (uniaxial negative), Dm = 2.75 g/cm3, Dcalc = 2.769 g/cm3 and H (Mohs) = 5.5. It is transparent and slightly yellow, has a good {100} cleavage, chonchoidal fracture, white streak and a vitreous lustre. It occurs in upper-mantle garnet-granulite xenoliths hosted by olivine nephelinite, from McBride Province, North Queensland, Australia. The empirical formula, derived from electron-microprobe analysis, is (Na1.06Ca2.86)(Al4.87Si7.13)O24 [(SO4)0.57(CO3)0.41]. Crystal-structure refinement shows disordered carbonate and sulfate groups along the fourfold axis. Silvialite is a primary cumulate phase precipitated from alkali basalt at 900−1000°C and 8−12 kbar under high fSO₂ and fO₂ . The name silvialite, currently used in literature to describe the sulfate analogue of meionite, was suggested by Brauns (1914).

Comparison of Microbial Biomass, Biodiversity, and Biogeochemistry in Three Contrasting Gold Mine Tailings Deposits

Abstract An interdisciplinary approach was used to assess the biogeochemistry of three deposits of gold mine tailings in Nopiming Provincial Park, Manitoba, Canada. Each depositional site has developed varying levels of natural revegetation over the past 70 years. Although the tailings are the products of processing similar carbonate-hosted quartz-carbonate shear zones by the same methods, the physical, chemical, and hydrogeological conditions varied among sites. The sample from the barren tailings area at the Central Manitoba site was lower in pH (4.87 ± 1.34) and higher in total sulfur (337 ± 166 μmol/g) and copper (44.5 ± 20.9 μ mol/g) than samples from the other two sites. Microbial activities have impacted the biogeochemical distribution of carbon, sulfur (total, sulfide, sulfate), and iron (total, Fe(II)) in the tailings at all three sites. The microbial communities were distributed throughout the tailings, but the biomass and biodiversity were greatest at the surface in the revegetated (Ogama-Rockland) and partially revegetated (Gunner) tailings. In contrast, the most barren set of tailings (Central Manitoba) had the greatest biomass and biodiversity in the middle layer (15 cm depth), which also had the greatest abundance of metals, anions, and carbon. The distribution of fatty acid methyl esters (FAME) in the tailings was dependent on both the depth and the individual characteristics of the site. The biomass and biodiversity correlated with the physicochemical conditions, particularly as affected by water movement and hydrology. The primary determinants limiting natural attenuation of the sites may be insufficient calcite buffering, hydrogeology, and the distribution of microbes, rather than a lack of microbes.

Scapolite cell-parameter trends along the solid-solution series

Abstract Scapolites are tetragonal framework aluminosilicates with the general formula M4T12O24A,the major constituents being M = Na + Ca, T = Si + Al, and A = Cl + CO3 + S-bearing anions, along with minor Fe, Sr, Ba, K, and H. Substitutions among the M, T, and A sites are independent and constrained only by net charge balance and maximum site occupancy. The cell parameters vary primarily with framework chemistry and Al-Si order and are not a strong function of the M- or A-site substitutions. End-member marialite has a = 12.06(1) and c = 7.551(5) Å, and meionite has a = 12.20(1) and c = 7.556(5) Å. Changes in cell- parameter trends in the series occur at Al3.6Si8.4O24 and Al4.7Si7.3O24 and are correlated with the locations of P42/n-I4/m phase transitions. The scapolite group can be divided into three isomorphous series: 9.0 > Si > 8.4, 8.4 > Si > 7.3, and 7.3 > Si > 6.0, each with its own patterns of Al-Si order. Because scapolites with the same Si content have variable cell parameters, there might be variable degrees of Al-Si order or a minor, secondary influence of the M- or A-site substituents.

27Al and 23Na NMR spectroscopy and structural modeling of aluminofluoride minerals

Abstract Simulations of high-resolution 19F-decoupled 27Al and 23Na magic-angle spinning nuclear magnetic resonance (MAS NMR) spectra of the aluminofluoride minerals, cryolite, cryolithionite, thomsenolite, weberite, chiolite, prosopite, and ralstonite combined with theoretical modeling have given accurate values of chemical shift (δiso), and quadrupolar interaction parameters (Cq and η), thereby eliminating ambiguities incurred by the complex nuclear interactions. These NMR data have been correlated with local electronic environments in the minerals, which were calculated using Full Potential Linearized Augmented Plane Wave (FP LAPW) modeling based on the structures from X-ray diffraction (XRD) data. This combination of NMR, XRD, and modeling techniques allowed the analysis and optimization of the crystal structures. The electronegativities and distances of neighboring ions, represented here by an environmental parameter χ, are shown to control δiso of both 23Na and 27Al. The calculations using χ, also show that the ions beyond the nearest neighbor play an important role in determining δiso of 27Al and 23Na in these aluminofluoride minerals, and the substitution of OH for F significantly affects the shielding around 27Al in prosopite and ralstonite. There is a positive correlation between the site distortion at the Na and Al sites and the values of Cq in these aluminofluoride minerals.

Lead exchange into zeolite and clay minerals: A 29Si, 27Al,23Na solid-state NMR study

Abstract Chabazite, vermiculite, montmorillonite, hectorite, and kaolinite were used to remove Pb, through ion exchange, from 0.01 M aqueous Pb(NO3)2 solutions. These minerals contained 27 (Nachabazite), 16, 9, 9, and 0.4 wt% of Pb, respectively, after equilibration with the solutions. Ion exchange reached equilibrium within 24 h for Na-chabazite and vermiculite, but in less than 5 min for montmorillonite and hectorite. Na-chabazite took up more Pb than natural (Ca, Na)-chabazite (7 wt% Pb), whereas no such difference was observed in different cation forms of the clay minerals. Calcite impurities, associated with the clay minerals, effectively removed Pb from the aqueous solutions by the precipitation of cerussite (PbCO3). 29Si, 27Al, and 23Na magic angle spinning (MAS) nuclear magnetic resonance (NMR), 23Na double rotation (DOR) NMR, and 23Na variable-temperature MAS NMR were used to study the ion exchange mechanisms. In Na-chabazite, cations in all three possible sites take part in the fast chemical exchange. The chemical exchange passes from the fast exchange regime to the slow regime at −80 to −100°C. One site contains a relatively low population of exchangeable cations. The other two more shielded sites contain most of the exchangeable cation. The exchangeable cations in chabazite and vermiculite were found to be close to the SiO4 and AlO4 tetrahedra, while those in the other clay minerals were more distant. Two sites (or groups of sites) for exchangeable cations were observed in hectorite. Lead tended to occupy the one which corresponds to the −8 ppm peak on the 23Na MAS NMR spectrum. The behaviour of the exchangeable cations in the interlayer sites was similar in all the clay minerals studied.

27Al NMR spectroscopy at multiple magnetic fields and ab initio quantum modeling for kaolinite

Abstract Diffraction methods indicate clearly that there are two crystallographic Al sites in kaolinite with different site symmetry. Many unsuccessful attempts have been made to resolve the two different Al sites in kaolinite by magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy since the early 1980s. This study attempts to resolve these sites, derive accurate quadrupolar coupling parameters at the two sites, and explain the reasons for the lack of separation by combining NMR spectroscopy at various fields with ab initio quantum modeling. At a high field such as 21.06 T, large chemical shift anisotropy and dipolar effects can overwhelm the quadrupolar interaction effects for sites with relatively small Cq values such as the two Al sites in kaolinite. The spectra will then display featureless lineshapes lacking the typical quadrupolar interaction characteristics. At lower fields, such as 4.68 T, the quadrupolar interaction effects become dominant, but due to the similarity of the two Al environments in kaolinite, as well as broadening by residual dipole-dipole and chemical shift anisotropy, the 27Al MAS NMR peaks still could not be separated. To resolve the two different Al sites spectroscopically, 27Al MAS NMR experiments at multiple magnetic fields, satellite transition NMR, and multiple-quantum MAS techniques have been utilized. Although these NMR experiments failed to resolve the two Al sites, the spectra have been interpreted with the aid of theoretical ab initio quantum mechanical modeling using full potential linearized augmented plane wave (FP-LAPW) model and the CASTEP software program. Average values of Cq, η, and δiso for the two Al sites were constrained to be 2.6 MHz, 0.75 and 6.25 ppm with high confidence.